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pzozulka

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Subnets and VLANs

I'm don't understand subnets and VLANs 100%, so I need a little bit of help. In the example below, the only thing that changed is the subnet mask on my WIN 7 PC.

My computer had the static IP settings below:
IP address: 10.0.64.4
Subnet: 255.255.255.0
Gateway: 10.0.64.1
DNS: 10.0.32.3

CAN ping anything in my own subnet/VLAN: DHCP scope=10.0.64.0, VLAN 640, range=10.0.64.3-14, router 10.0.64.1, subnet=255.255.255.240

CAN ping anything in: DHCP scope=10.0.24.0, VLAN 240, range=10.0.24.3 - 30, router = 10.0.24.1, subnet=255.255.255.224

CANNOT ping anything in: DHCP scope= 10.0.64.16, VLAN 642, range=10.0.64.19 - 30, router=10.0.64.17, subnet=255.255.255.240

CANNOT ping anything in: DHCP scope=10.0.64.32, VLAN 644, range=10.0.64.35-38, router=10.0.64.33, subnet=255.255.255.248

HOWEVER, when I changed my settings to allow DHCP to automatically get an IP, I had the settings below:

IP: 10.0.64.4
Subnet: 255.255.255.240
Gateway: 10.0.64.1
DNS: 10.0.32.3

With these settings I was able to ping ALL subnets/VLANs. The only thing that changed is the subnet mask. Why am I now able to (all of  sudden) ping all IPs.
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Don Johnston
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My computer had the static IP settings below:
IP address: 10.0.64.4
Subnet: 255.255.255.0
Gateway: 10.0.64.1

This means your computer thinks that it is on the 10.0.64.0/24 network. Which means that it expects that it is on the same network/broadcast domain/VLAN with devices that have IP addresses 10.0.64.1-254.

CAN ping anything in my own subnet/VLAN: DHCP scope=10.0.64.0, VLAN 640, range=10.0.64.3-14, router 10.0.64.1, subnet=255.255.255.240

Yep. Those device are within the range of addresses that your computer expects to see on it's network.

CAN ping anything in: DHCP scope=10.0.24.0, VLAN 240, range=10.0.24.3 - 30, router = 10.0.24.1, subnet=255.255.255.224

That's expected too. Those devices are seen as being on different networks so your PC will forward that traffic to the default-gateway which then routes the packets to the correct network.

CANNOT ping anything in: DHCP scope= 10.0.64.16, VLAN 642, range=10.0.64.19 - 30, router=10.0.64.17, subnet=255.255.255.240

That's expected too. You PC thinks those addresses are local. The problem is they're actually on different networks.

CANNOT ping anything in: DHCP scope=10.0.64.32, VLAN 644, range=10.0.64.35-38, router=10.0.64.33, subnet=255.255.255.248

Same as previous.

HOWEVER, when I changed my settings to allow DHCP to automatically get an IP, I had the settings below:

IP: 10.0.64.4
Subnet: 255.255.255.240
Gateway: 10.0.64.1

With these settings I was able to ping ALL subnets/VLANs. The only thing that changed is the subnet mask. Why am I now able to (all of  sudden) ping all IPs.

Now you are on the 10.0.64.0/28 network. Your PC thinks the only thing that's local is 10.0.64.1-14. Because it knows the 10.0.64.17 and higher addresses aren't local, it forwards those packets to the default-gateway.

Basically, when you had an address of 10.0.64.4/24, you had the incorrect mask.
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pzozulka

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CANNOT ping anything in: DHCP scope= 10.0.64.16, VLAN 642, range=10.0.64.19 - 30, router=10.0.64.17, subnet=255.255.255.240


That's expected too. You PC thinks those addresses are local. The problem is they're actually on different networks.

OK so I understand that when i'm on a different network than another PC, it forwards packets to the default gateway, and the routers work things out.

However, when i'm on 10.0.64.0/24 network, I should be able to communicate with all PCs in the range of 10.0.64.1 - 254. So when a PC comes along with IP 10.0.64.25, it does fall into my IP range, and I should be able to ping it. I still don't understand why I am not able to.
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Don Johnston
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I think your last post was cut off.
No. I was thinking of an analogy but it didn't jell. :-(
:) sounds good. It made sense either way.